Field of the Invention
The disclosure provides shaped catalyst materials useful for the sour gas shift reactions and methods for using such catalyst materials.
Description of Related Art
Synthesis gas, also termed syngas, is generally composed of hydrogen and carbon oxides (CO and CO2) and is an important feedstock in the chemical and energy industries. It may be generated by gasification of carbonaceous feedstocks such as coal, petroleum coke or other carbon-rich feedstocks using oxygen or air and steam at elevated temperature and pressure. Gasification alone can provide an undesirably high ratio of CO to H2. To remedy this, the water-gas shift reaction:H2O+CO→H2+CO2 can be used to decrease the ratio of CO to H2. Specialized catalysts, such as copper-based catalysts, iron-based catalysts and nickel-based catalysts, are typically used in the water gas shift reaction. However, when the synthesis gas is contaminated with one or more sulfur compounds, as is common when coal-based feedstocks are used, such catalysts can become inactivated. Accordingly, sulfur-tolerant shift catalysts have been developed, based on, for example, cobalt and molybdenum. When the water-gas shift reaction is performed in the presence of sulfur impurities, it is known as a “sour gas shift”. Sour gas shift reactions are generally exothermic, and are conventionally allowed to run adiabatically, with control of the exit temperature governed by feed gas inlet temperature and composition. With an increase in temperature, however, undesirable side reactions can occur, particularly methanation. Moreover, unsafe reaction conditions and the possibility of catastrophic reaction runaway increase with increasing temperature. The problem of exothermicity is especially important in cases where the inlet gas stream has a high CO concentration. But more and more technologies used for gasification generate high CO concentration (over 60%), well over the 40% CO concentration at which typical industrial sour gas shift reactions run manageably and safely. To avoid side reactions and unsafe operation, the shift reaction is typically performed with considerable amounts of added steam. However, such steam addition can complicate reaction processes, and may require catalysts with improved characteristics, such as increased geometric surface area, improved diffusion efficiency, enhanced heat transfer and reduced pressure drop.
These characteristics may be achieved with a hollow shaped catalyst. But hollow shaped catalysts typically suffer from decreased mechanical integrity and stability, which are essential for use in large scale reactors. A hollow shaped catalyst with insufficient mechanical integrity is not generally useful in industrial processes even if its performance characteristics are otherwise superior. Currently, there are no commercially-available hollow shaped catalysts having the mechanical integrity and stability necessary for the high-steam conditions of an industrial-scale water gas shift process.